[PATCH net-next] tcp: fix out-of-bounds access in ULP sysctl

[PATCH net-next] tcp: fix out-of-bounds access in ULP sysctl

[Jakub Kicinski]

KASAN reports out-of-bound access in proc_dostring() coming from
proc_tcp_available_ulp() because in case TCP ULP list is empty
the buffer allocated for the response will not have anything
printed into it.  Set the first byte to zero to avoid strlen()
going out-of-bounds.

Fixes: 734942cc4ea6 ("tcp: ULP infrastructure")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
---
 net/ipv4/tcp_ulp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_ulp.c b/net/ipv4/tcp_ulp.c
index e855ea70819b..2417f55374c5 100644
--- a/net/ipv4/tcp_ulp.c
+++ b/net/ipv4/tcp_ulp.c
@@ -88,6 +88,7 @@ void tcp_get_available_ulp(char *buf, size_t maxlen)
 	struct tcp_ulp_ops *ulp_ops;
 	size_t offs = 0;
 
+	*buf = '\0';
 	rcu_read_lock();
 	list_for_each_entry_rcu(ulp_ops, &tcp_ulp_list, list) {
 		offs += snprintf(buf + offs, maxlen - offs,
-- 
2.11.0

Re: [PATCH net-next] tcp: fix out-of-bounds access in ULP sysctl

[David Miller]

From: Jakub Kicinski <jakub.kicinski@netronome.com>
Date: Thu, 22 Jun 2017 18:57:55 -0700

> KASAN reports out-of-bound access in proc_dostring() coming from
> proc_tcp_available_ulp() because in case TCP ULP list is empty
> the buffer allocated for the response will not have anything
> printed into it.  Set the first byte to zero to avoid strlen()
> going out-of-bounds.
> 
> Fixes: 734942cc4ea6 ("tcp: ULP infrastructure")
> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

Applied, thanks.